This disclosure relates to a suspension system and valve for a multi-axle vehicle, and more particularly to providing a single valve that replaces three valves as used in a known suspension system. More particularly, the disclosure is directed to a normally open, pilot operated valve that delivers supply air pressure upon receiving a sustained air pressure input of a pilot signal and, using an inversion function, the valve dumps delivery pressure through a high capacity exhaust upon receiving the pressure input of a secondary control signal. A hold function of the valve traps a small amount of delivery air pressure by closing the exhaust valve.
Federal regulation, namely Title 49 of the Code of Federal Regulations, Section 393.207, states that “the air suspension exhaust controls must not have the capability to exhaust air from the suspension system of one axle of a two-axle air suspension trailer unless the controls are either located on the trailer, or the power unit and trailer combination are not capable of traveling at a speed greater than ten miles per hour while the air is exhausted from the suspension system.” One proposed solution is outlined in U.S. Pat. No. 5,052,713, the disclosure of which is incorporated herein by reference. The '713 patent is directed to a vehicle suspension system such as used in multi-axle tractor-trailers and other multi-axle vehicles. When maneuvering a trailer in a confined area such as a loading dock, torque is exerted on the trailer frame. One solution to the torque issue is to remove the load from all but one axle. The '713 patent teaches that air should be exhausted from the air bags on all but one axle in order to improve maneuverability at low speeds or during tight turns. Moreover, and per the federal regulation, the load must be redistributed to the multiple axles once the tight turn maneuvering is complete. Otherwise, the potential exists that a single axle may be overloaded, since the load has not been shifted to multiple axles. The overloading could result in potential damage to the trailer frame or dynamic loading encountered by the vehicle.
Although the '713 patent provides one solution, there are some downsides to this methodology and system. First, there is risk of damage to the air bags when all air is exhausted therefrom. The air bags may be pinched. Thus, there is a need to hold pressure in the air bags while the vehicle is maneuvering at slow speeds.
A current solution is to use a number of conventional valves to dump air from air bags of a first or rearward trailer axle suspension system, and thereby take weight off that axle. This allows the trailer to pivot on the second or front trailer axle during the turn. Once the turn is complete, air is then returned to the rear axle suspension.
Using three (3) separate valves to perform this function is not cost effective. Multiple valves add overall system costs, add complexity to installation, and also raise attendant maintenance issues. Thus, a need exists for a single, multi-function valve for use primarily on multi-axle semi trailers equipped with air suspensions, and particularly use of such a valve in a system that exhausts air from a rearward axle air suspension system when the vehicle is maneuvering at slow speeds, reduces the load on the rear axle, and thus reduces damaging forces that effect tire wear and suspension component wear. The valve must be able to deliver supply air pressure upon receiving a sustained air pressure input of a pilot signal. Additionally, as part of an inversion function, the valve must dump the delivery pressure through a high capacity exhaust upon receiving the pressure input of a secondary control signal. Last, the valve must provide a hold function that traps a small amount of delivery air pressure.